Power Supply/Mute - Fender BASSBREAKER 15 Combo Service Manual

POWER SUPPLY/MUTE

The Power Supply circuitry is found on the POWER
SUPPLY PCB. Its circuitry is typical of a Fender
tube amplifier with a choke input filter. The second-
ary side of the Power Transformer consists of 3
windings: high-voltage winding, low-voltage winding
and heater winding.
The high voltage red/red secondary winding is used
to generate the high voltage DC power supplies in
the amplifier. The high voltage DC power supply is
energized through a full-wave bridge rectifier con-
figuration to filter cap C80.
between C80 & C42. The output of this supply filter
provides B+ to the plates of the EL84 power tubes.
The "voltage-drop" resistors R58, R59, & R61,
along with their associated filter capacitors C43,
C44, & C49, subsequently provide the DC screen-
grid voltages for the power tubes and plate voltages
for the preamp tube stages in the design. These
supplies are routed to the TUBE PCB circuitry
through 18 AWG wiring between the two PCBs.
The low voltage brown/brown secondary winding
feeds a full-wave bridge & filter configuration to cre-
ate input DC voltages for regulators U5-U7. These
heat-sinked ICs generate the low voltage +/-15.6V
& +5V DC power supplies. A primary function of the
U5 & U6 power supplies is to provide DC filament
drive to the preamp tube heaters (V3-5). The DC
bipolar filament voltages couple to the heaters
.
A choke is inserted
BASSBREAKER™ 15
(This is the model name for warranty claims)
through R63 & R64 on the POWER SUPPLY PCB.
A cable connects this supply to the filaments on the
TUBE PCB at P29. A cable also connects the low
voltage supplies to the REAR PANEL PCB & CON-
TROL PCB to power their op-amp analog signal
processing & control circuitry.
powers the reverb card that is mounted as a daugh-
ter card on the POWER SUPPLY PCB.
The green/green heater secondary winding produc-
es a 6.8VAC power supply that energizes the EL-84
power tube (V1 & V2) heater filaments. This sec-
ondary does not supply preamp tube filament drive
as explained above. This secondary is connected
to terminals on the TUBE PCB.
The POWER INDICATOR LED installed inside the
control panel jewel. It is controlled by the LM555
timer installed at U4. U4's output drives this LED
through R46 via its connections to the red & white
wires routed from the rear panel to the control pan-
el.
If the MUTE is enabled, the LED will flash several
times per second. When this is flashing, audio is
not delivered to the power amp input and nothing
should be audible. This allows "silent recording"
capability through the rear panel's LINE OUT con-
nection.
If the MUTE is disabled, the amplifier should be ca-
pable of delivering audio through an internal &/or an
external speaker connection.
8
The +5V supply